All electromagnetic types of electromechanical transducers for converting energy between a mechanical form and an electrical form operate on the same basic principles utilizing a time change of magnetic flux through a coil of wire. The differences between them lie in their practicality and relative efficiency.
In order to optimize efficiency and practicality, a variety of different parameters must be considered and optimized. For example, in a linearly reciprocating machine, such as a linear alternator, it is desirable to minimize the mass which must be driven in reciprocation in order to minimize the momentum which must be overcome by the driving forces. Similarly, it is desirable to minimize the total mass of an electrical alternator in order to provide the maximum ratio of energy output to alternator weight.
Another goal in the design of such electromagnetic, electromechanical transducers is to maximize the electric current at which the machine can operate before the transformer iron, which is used to provide a high permeance flux path, begins to saturate. The flux causing saturation arises from two components, one from the source of magnetic flux, such as a permanent magnet and the other from the current induced in the armature winding. The latter source, referred to as the armature reaction flux, is proportional to the armature current divided by air gap distance. Thus, reducing the armature reaction flux by increasing the number of working gaps permits a higher operating current before saturation.
Another goal in the design of a linear alternator is that it permits the armature windings to be easily and conveniently wound without winding through a narrow gap or forming the core in separable parts which are connected after the coil is wound to form an unwanted gap at the junction.